Strategies needed to address insecticide resistance in malaria-endemic countries

Despite the significant decrease in malaria-associated morbidity and asymptomatic parasite carriage after implementation of insecticide-treated bed nets across all age groups in the village of Dielmo in Senegal, researchers observed a rebound in morbidity and malaria incidence rates 30 months after implementation.

The rebound in malaria incidence was highest among children (aged 10 to 14 years) and in adults. Overall, this population accounted for 45 (63%) of 71 malaria cases in 2010 vs. 126 (33%) of 384 cases in 2007 and 2008 (P<.0001).

“We recorded a rebound of malaria morbidity temporally related to the emergence of pyrethroid resistance in Anopheles gambiae,” Jean-François Trape, MD, of the research unit on emerging infectious and tropical diseases at the Institut de Recherche pour le Développement, in Dakar, Senegal, and colleagues wrote in the study.

“These findings are of great concern, since they support the idea that present methods and policies will not sustain — at least in older children and adults — a substantial decrease in malaria morbidity in many parts of Africa where A. gambiae is the major vector and acquired clinical immunity is a key epidemiological factor,” they said. “Strategies to address the problem of insecticide resistance and to mitigate its effects must be urgently defined and implemented.”

In the longitudinal study, the researchers assessed the extent to which long-lasting insecticide (deltamethrin)-treated nets (LLINs) and the use of artemisinin-based combination therapies may reduce malaria morbidity among 504 participants between January 2007 and December 2010. Participants were monitored daily for fever; and mosquito captures were monitored monthly. A total of 464 malaria cases were reported.

In July 2008, participants were provided with LLINs. Eighteen months after the introduction of LLINs, when artemisinin-based combination therapy alone was used for malaria control, malaria incidence averaged 5.45/100 person-months (95% CI, 4.90-6.05). After distribution of LLINs, incidence significantly decreased to 0.41/100 person-months (95% CI, 0.29-0.55) between 2008 and 2010. However, malaria incidence then increased to 4.57/100 person-months (95% CI, 3.54-5.82) by the end of 2010.

In addition, 37% of mosquitoes carrying A. gambiae demonstrated deltamethrin resistance during 2010. The prevalence of the Leu1014Phe kdr-resistant mutation increased from 8% in 2007 to 48% in 2010 (P=.0009).

“The effect of the introduction of LLINs on the survival of A. gambiae and A. arabiensis in 2008 and 2009 and the change in 2010 when the parity of these vectors returned to pre-intervention levels suggest that pyrethroid resistance could be a major factor in the increase in malaria morbidity in 2010,” the researchers wrote.

In an accompanying editorial, Joseph Keating, PhD, and Thomas P. Eisele, MD, both of the department of global health systems and development at Tulane University, wrote: “Trape and colleagues have reinforced the importance of monitoring insecticide resistance, drug resistance, and changes in malaria epidemiology within the context of intervention-suppressed transmission in Africa — all of which have direct relevance for guiding malaria control policy.”

For more information:

Keating J. Lancet Infect Dis. 2011;doi:10.1016/S1473-3099(11)70212-2.

Trape JF. Lancet Infect Dis. 2011;doi:10.1016/S1473-3099(11)70194-3.

Disclosure: This research was funded by Institut de Recherche pour le Développement and the Pasteur Institute of Dakar.

Follow InfectiousDiseaseNews.com on Twitter.